Prior to 1970, all of the Nigerian states had their own coats of arms and flags. The state flag
was modeled on the Nigerian national flag but with the
state coat of arms in the centre of the white stripe. These state flags
were adopted in 1967 and abolished in 1970. Since 1970 only the Nigerian
national coat of arms and national flag may be used as symbol of a state.
Source: Enzyklopädie der staatlichen Wappen und Flaggen (Encyclopaedia
of State Coat of Arms and State Flags), Volume 6.Jens Pattke, 09 July 2006